Researchers at EPFL (École polytechnique fédérale de Lausanne ) and UNIL (Université de Lausanne) have discovered a faster way for six-legged robots to move on flat ground, provided they don’t have the adhesive pads used by insects to climb walls and ceilings.

This suggests designers of insect-inspired robots should ditch the tripod-gait paradigm and instead consider other possibilities including a new locomotion strategy called the “bipod gait.”

“We wanted to determine why insects use a tripod gait and identify whether it is, indeed, the fastest way for six-legged animals and robots to walk,” says Pavan Ramdya, co-lead and corresponding author of the study.

To test the various combinations, the researchers used an evolutionary-like algorithm to optimize the walking speed of a simulated insect model based on Drosophila melanogaster, a commonly studied insect in biology. Step-by-step, this algorithm sifted through many different possible gaits, eliminating the slowest and shortlisting the fastest.

The researchers found that the common insect tripod gait did emerge when they optimized their insect model to climb vertical surfaces with adhesion on the tips of its legs. By contrast, simulations of ground-walking without the adhesiveness of insects’ legs revealed that bipod gaits, where only two legs are on the ground at any given time, are faster and more efficient – although in nature no insects actually walk this way.

The researchers then built a six-legged robot capable of employing either the tripod or bipod gait. The bipod gait was again demonstrated to be faster, corroborating the simulation algorithms’ results.

The experimenters also examined real insects. To see if leg adhesion might also play a role in the walking coordination of real flies, they put polymer drops on the flies’ legs to cover their claws and adhesive pads – as if the flies were wearing boots – and watched what happened. The flies quickly began to use bipod-like leg coordination similar to the one discovered in the simulation.

“This result shows that, unlike most robots, animals can adapt to find new ways of walking under new circumstances,” says Robin Thandiackal, a co-lead author of the study. “There is a natural dialogue between robotics and biology: Many robot designers are inspired by nature and biologists can use robots to better understand the behavior of animal species. We believe that our work represents an important contribution to the study of animal and robotic locomotion.”